In highly efficient two-cycle engines with one or more cylinders, attempts have been made to provide independent scavenging of the cylinder(s) by fuel-free fresh air and introduction of atomized liquid fuel into the cylinder(s), these two operations being performed at successive points in time precisely determined by the engine operating cycle.
The atomized fuel can be introduced into the cylinder by a pneumatic injection device comprising an injector terminating in the cylinder and equipped with a valve, controlled by a cam which opens and closes the valve, a means for supplying the injector with liquid fuel, and a source of compressed air to atomize and inject the fuel when the injector opens.
The cylinder is scavenged by fresh air from a pump housing having lower part communicating with the cylinder, so that the piston, as it moves in the cylinder, compresses the air in the housing as it approaches bottom dead center. Two pipes connecting the pump housing to the intake ports of the cylinder transfer the compressed air to the cylinder, with the compressed air entering the cylinder being scavenged when the intake ports are uncovered by the piston as it approaches bottom dead center.
It has been proposed that fuel be injected pneumatically by using the compressed air from the pump housing to atomize and inject the fuel. For this purpose, the pump housing can be connected to the injector by a pipe containing a check valve. The part of the pipe located downstream of the check valve can itself constitute a compressed air reservoir or can be connected to such a reservoir. When the injector opens, a certain quantity of compressed air is used to atomize the fuel and inject it into the cylinder. The compressed air reservoir is recharged by opening the valve when the pressure is close to maximum in the pump housing.
A device of the aforementioned type eliminates the supplementary compressed gas source, however, requires a connecting pipe between the pump housing and the injector and possibly a reservoir communicating with said connecting pipe.
In multicylinder fuel-injected engines, it has been proposed to use hot pressurized gases tapped from a cylinder to atomize the fuel in another cylinder of the engine. Injection occurs at the cylinder intake valve through which the fuel-air mixture is added to fill the cylinder. The effect of the hot tapped gases is limited to ensuring the atomization and possibly the vaporization of the liquid fuel introduced into the cylinder when the intake valve opens, by mixing with the incoming air and being drawn into the cylinder.
In this case, in contrast to the case of two-cycle engines and the like, fresh scavenging air is not introduced into the cylinder independently of the fuel, and the fuel itself is not introduced under pressure by a pneumatic injector independent of the device for introducing air into the cylinder.
Heretofore, pneumatic injection has always employed either an auxiliary compressed air supply or a connecting pipe between the pump housing and the cylinder and possibly a reservoir for storing the compressed air.